Synchronization of devices in a RFID communications environment

ABSTRACT

An adaptive wakeup methodology may be implemented to allow an radio frequency identification (RFID) tag to stay synchronized with periodic radio frequency (RF) interrogator polling signal while at the same time optimizing power consumption. A receiver (or transceiver) component of a RFID tag may only be operated when an interrogator polling signal is expected, and in a manner that reduces the amount of time between when the receiver or transceiver is turned on and when the interrogator polling signal is received (i.e., the receive buffer time). At other times, the RFID tag may be placed in a low power consumption sleep state. The amount of time that the RFID tag spends in such a low power sleep state before waking and receiving the following interrogator polling signal may also be optionally adjusted, e.g., to fit characteristics of a given situation and/or to re-synchronize a given aRFID tag with first band transmissions from an aRFIDI.

FIELD OF THE INVENTION

This invention relates generally to data communication, and moreparticularly to separation of data communication in high densityenvironments.

BACKGROUND OF THE INVENTION

As defined by the FCC, an ultra-wideband (UWB) signal is an antennatransmission in the range of 3.1 GHz up to 10.6 GHz at a limitedtransmit power of −41.3 dBm/MHz with an emitted signal bandwidth thatexceeds the lesser of 500 MHz or 20% of the center frequency. UWBsignals are currently employed for high-bandwidth, short rangecommunications that use high bandwidth radio energy that is pulsed atspecific time instants.

Applications for FCC-defined UWB transmissions include distance-basedlocation and tracking applications, and localization techniques thatemploy precision time-of-arrival measurements. Examples of such UWBapplications include radio frequency identification (RFID) tags thatemploy UWB communication technology for tracking, localization andtransmitting information. Other types of UWB applications includeprecision radar imaging technology. Inventory tracking has beenimplemented through the use of passive, active and semi-passive RFIDdevices. These devices have widespread use, and typically respond tointerrogation or send data at fixed intervals.

A high density active radio frequency identification (aRFID) environmentcan easily exceed 1000 aRFID tags for certain application installations,such as cattle feedlot applications where individual cows are eachtagged with an aRFID tag. Currently, aRFID installations such as thesemay be implemented using a maximum of approximately 1000 aRFID tags pereach RFID receiver that is provided for the installation. However, aRFIDenvironments may routinely contain in excess of 40,000 tags within a 1to 2 sq mile area. One previous attempt that has been made to reliablyreceive and process tag data, and to perform geolocation calculations insuch environments, is to use software-only coding schemes in order tohelp distinguish between multiple tags. This method typically works upto the point where available bandwidth is exceeded due to the number ofbits being transmitted (˜100 bits per tag transmission) and the numberof tags in the environment (˜1000). Existing RFID tag geolocationtechnologies employ RFID tags which typically report data at a fixedrate, which is acceptable for low tag density environments (i.e., tagdensity less than approximately 1000) where interleaved and collidingpackets are not problematic.

Traditional time difference of arrival (TDOA) techniques that areemployed to locate emitters, such as transmitting RFID tags, requirethat the absolute time of arrival (TOA) of an emitted signal at each oftwo or more receivers be recorded and the difference taken, or requirethat the two signals be processed using a cross correlation method. Theprimary source of error in determining the absolute TOA is the accuracywith which the arrival time of the emitted signal may be measured ateach receiver. Although a high degree of timing accuracy can, inprincipal, be obtained by employing highly synchronized clocks at eachreceiver (e.g., using synchronized atomic clocks), this can be a veryexpensive option. Use of a cross correlation method is appropriate onlyfor narrow band signals and also lacks a high degree of precision.

SUMMARY OF THE INVENTION

Disclosed herein are systems and methods for data separation, which maybe employed to reliably receive and process RFID tag data, and/or toperform tag geolocation calculations in environments where the totalnumber of RFID tags exceeds 1000, for example as may be encountered inRF signal environments where multiple RFID tags are tracked, localizedand/or employed to transmit information. Examples of such RFIDenvironments include, but are not limited to, high density aRFIDenvironments having a total number of aRFID tags that exceed 1000, e.g.,cattle feed lot applications where over 1000 individual cows are eachtagged with an aRFID tag. However implemented, each RFID tag device mayhave a unique identifier that is associated with an object to which itis associated (e.g., attached or otherwise coupled) such that thelocation of the RFID tag is representative of the location of theobject. In this manner, a user or other entity may readily identify thecurrent location of a particular object, based on the location of itsassociated transmitting RFID tag. The disclosed systems and methods maybe implemented in a variety of applications (e.g., asset or inventorytracking, sensor networks, geolocation devices, etc.) and may beimplemented using passive, active and/or semi-passive RFID tag devicesthat respond to interrogation and/or send data at fixed intervals. Inthis regard, semi-passive RFID tag devices may remain in a sleep modeuntil receipt of a signal (e.g., interrogator polling signal) that wakeup the device for transmission using internal battery poweredtransmitter onboard the semi-passive tag.

In one exemplary embodiment the disclosed systems and methods may beimplemented for data separation in a high density aRFID environment thatincludes greater than about 10,000 tags (e.g., greater than about 40,000tags within a 1 square mile area), and/or using a receiver to RFID tagratio of less than about 1 receiver to 2500 tags (1/2500). In anotherexemplary embodiment, the disclosed systems and methods may beimplemented to allow an RFID tracking environment to employ a totalnumber of RFID tags that exceeds about 1000 tags, and/or in which theindividual tag transmission rate exceeds about 100 bits per RFID tagtransmission. In yet another exemplary embodiment, the disclosed systemsand methods may be implemented to allow an RFID tracking environment toemploy up to 100,000 RFID tags with an individual tag transmission rateup to about 100 bits per RFID tag transmission, it being understood thatgreater than 100,000 RFID tags may be employed in an RFID trackingenvironment and/or tag transmission rates of greater than 100 bits perRFID tag transmission may be possible in other embodiments.

The disclosed systems and methods may be implemented using a first bandthat is multiple channel-based, meaning that the RF spectrum of thefirst frequency band is broken up or divided into a plurality ofseparate channels, and first band communications may be achieved betweenany two devices of the disclosed systems and methods using a subset ofthe channels within the first band (e.g., a single one of the channels,two of the channels, etc.) and/or in narrow band fashion by using asub-set of the channels within the band, e.g., using less than three ofthe channels. In this way, a first channel of the first band may be usedfor communication between a first pair of system devices and a secondchannel of the first band may be used for communication between a secondpair of system devices. Such a multi-band RFID tag system may be furtherconfigured to have a second band (e.g., wide band such as UWB)transmitter, e.g., for responding to RFID interrogation signals from aninterrogator. The disclosed systems and methods may also employ a secondband frequency band that is non-channel based, meaning that the RFspectrum of the second frequency band is not broken up or divided upinto separate channels, but rather the communication signals are spreadacross the second frequency band such that the undivided second band maybe used by the RFID tag system for all second band communicationsbetween devices of the system. One example of a multiple channel-basedfirst band is a narrow band frequency modulation (NBFM) frequency bandhaving a plurality (e.g., 50) channels, and one example of a nonchannel-based second band is a pulse-based frequency band such as UWB.

Features that may be implemented in various possible embodiments of thedisclosed systems and methods include, but are not limited to, a firstband (e.g., Narrow Band Frequency Modulation “NBFM”) channelizedinterrogator, spatial diversity separation technique, frequencydiversity separation technique, and/or multi-band aRFID tags thatreceive data using a first band of signals (e.g., NBFM signals) and onlytransmit using a second band of signals (e.g., UWB signals) wheninterrogated. Further features that may be implemented include, but arenot limited to, wireless synchronization of individual aRFID tagcircuitry with a first band interrogator to minimize operating time of afirst band receiver of the individual aRFID tag.

In one exemplary embodiment, an active RFID interrogator (aRFIDI) systemmay be provided that combines spatial and frequency separationtechniques in order to reduce the aRFIDI system tag transmissiondensity, e.g., by a factor of about 400 in any one second interval. Suchan aRFIDI system may be positioned, for example, at or near the centerof a master coverage area (e.g., livestock feed lot, cultivated field,race track, hospital, warehouse, prison, city block, sports stadium,amusement park, airport, train station, shipyard, shop, factory,library, armory, military base, police station, etc.) to be covered byaRFID communications between the aRFIDI system and multiple tags (e.g.,which may be associated with individual livestock, farm equipment, racecars, trucks, rental cars and other vehicles, hospital patients,warehouse articles/boxes, library books, legal documents, tools,machines, guns or other weapons and accessories therefor, prisoners,sports players or fans, amusement park patrons, baggage and/orpassengers, ships or cargo, etc.) that may roam throughout the givenmaster coverage area.

The aRFIDI system may be provided with multiple antenna panels (or othertype of directional antenna or directional signal transmission systemconfiguration) that are spaced so that each panel covers a desired angleor area of coverage for selective signal communication (signaltransmission and/or reception) within a sector of the overall mastercoverage area, e.g., eight 45 degree coverage antenna panels that areequally spaced so as to cover a full 360 degrees of an overall mastercoverage area in eight sectors, it being understood that other sectorgeometries or shapes (i.e., other than pie-shaped) are possible, and/orthat other numbers of sectors provided within a master coverage area(i.e., greater or lesser than eight) are also possible. An aRFIDI systemmay be further configured to transmit on each of a selected number ofmultiple pre-defined channels of a first band (e.g., 50 pre-defined NBFMchannels) in each one of the sector coverage areas defined by a givenantenna panel. The transmit time by the aRFIDI system on each of thepredefined first band channels in a given sector coverage area may beshared with the other predefined first band channels during a selectedtransmission time interval allocated for the given sector coverage areasuch that a signal transmission occurs on each of the multiple firstband channels within the given sector coverage area once during theallocated time interval.

Within each sector coverage area of the overall master coverage area,roaming aRFID tags having assigned reception channels corresponding toone of the predefined first band channels may be interrogated using thismethodology. In this regard, each of the multiple roaming aRFID tags maybe configured to receive on one of the predefined first band channels,with each of the multiple predefined first band channels being assignedto at least one aRFID tag, and possibly more than one tag. Each of themultiple aRFID tags may have the capability to move from one sectorcoverage area to another sector coverage area by virtue of the host towhich they are attached (e.g., livestock, vehicles, persons, baggage,ships, etc.) such that at any given time, the aRFID tags present withina given sector coverage area have a first band receive capability thatis randomly distributed between the multiple predefined first bandchannels. When each aRFIDI system tag present within a given sectorcoverage area receives a first band interrogator signal from the aRFIDIsystem, a second band component (e.g., UWB component) of the tag is thentasked to transmit a response signal by a second and different band thanthe first band, i.e., each aRFIDI system tag will not transmit itssecond band response signal until interrogated over the first bandchannel by the aRFIDI system.

In one exemplary embodiment, an adaptive wakeup scheme or methodologymay be implemented to allow an aRFID tag to stay synchronized with anaRFIDI system while at the same time optimizing power consumption.Depending on the particular configuration of a given aRFID tag, thebattery life of an aRFID tag may be greatly reduced by first band signalreceiving operations. Thus, in this exemplary embodiment, a first bandreceiver (or transceiver) component of an aRFID tag may only be operatedwhen a first band packet is expected from an aRFIDI system, and in amanner that reduces the amount of time between when the first bandreceiver is turned on and when the first band packet is received (i.e.,the receive buffer time). At other times, the aRFID tag may be placed ina low power consumption sleep state. The amount of time that an aRFIDtag spends in such a low power sleep state before waking and receivingthe following interrogate packet (i.e. when an aRFIDI system is sendingout polling packets at a known rate) may also be optionally adjusted,e.g., to fit characteristics of a given situation and/or tore-synchronize a given aRFID tag with first band transmissions from anaRFIDI. Thus, the disclosed systems and methods may be implemented in amanner that allows a given aRFID tag to receive packets from an aRFIDIsystem within a given receive buffer time, while also correcting forclock drift between the aRFIDI system and the given aRFID tag.

In one respect, disclosed herein is a method of operating a radiofrequency identification (RFID) tag within a radio frequencyidentification (RFID) communication environment, including: providing atleast one RFID tag configured to receive periodic first band RF signalinterrogator polling signals to transmit second band RF signal responsesignals in response thereto, the first band being a multiplechannel-based frequency band and the second band being a non-channelbased frequency band. The method includes repeatedly and alternatelyperforming the following two steps: operating the RFID tag in a timedlow power sleep mode for a predefined sleep time during which the RFIDtag does not listen for transmitted first band RF signal interrogatorpolling signals, and then waking the RFID tag to operate in a timedpowered up listening mode for a predefined tag listening time duringwhich the RFID tag actively listens for transmitted first band RF signalinterrogator polling signals; and the method may further includedynamically adjusting the length of the predefined sleep time beforeagain waking the RFID tag to the listening mode.

In another respect, disclosed herein is a frequency identification(RFID) tag system, including: first band receiver or transceivercircuitry configured to receive periodic first band RF signalinterrogator polling signals and second band transmitter circuitryconfigured to transmit second band RF signal response signals inresponse thereto, the first band being a multiple channel-basedfrequency band and the second band being a non-channel based frequencyband. The system may further include at least one processing device torepeatedly and alternately perform the following two steps: operate thecircuitry of the RFID tag in a timed low power sleep mode for apredefined sleep time during which the first band receiver ortransceiver circuitry does not listen for transmitted first band RFsignal interrogator polling signals, and then wake up circuitry of theRFID tag to operate in a timed powered up listening mode for apredefined tag listening time during which the first band receiver ortransceiver circuitry actively listens for transmitted first band RFsignal interrogator polling signals. The processing device may also beconfigured to dynamically adjust the length of the predefined sleep timebefore again waking circuitry of the RFID tag to the listening mode.

In another respect, disclosed herein is a method of operating a radiofrequency identification (RFID) tag within a radio frequencyidentification (RFID) communication environment, including: alternatelyoperating at least one RFID tag between a non-synchronized state with aperiodic interrogator polling signal and a synchronized state with aperiodic interrogator polling signal, the RFID tag being configured toreceive periodic first band RF signal interrogator polling signals andto transmit second band RF signal response signals in response thereto,the first band being a multiple channel-based frequency band and thesecond band being a non-channel based frequency band. Thenon-synchronized state of the method may include: operating the RFID tagin a timed non-synchronized low power sleep mode for a predefinednon-synchronized sleep time during which the RFID tag does not listenfor transmitted first band RF signal interrogator polling signals, thenwaking up the RFID tag to perform one or more tag processing operations,then returning the RFID tag to the timed non-synchronized low powersleep mode for the predefined non-synchronized sleep time if the numberof immediately previous consecutive sleep times is less than apredefined threshold, or operating the RFID tag in a timed powered upnon-synchronized listening mode for a predefined non-synchronized taglistening time during which the RFID tag actively listens fortransmitted first band RF signal interrogator polling signals if thenumber of immediately previous consecutive sleep times is greater thanor equal to a predefined threshold. The synchronized state of the methodmay include: operating the RFID tag in a timed synchronized low powersleep mode for a predefined synchronized sleep time during which theRFID tag does not listen for transmitted first band RF signalinterrogator polling signals, then waking up the RFID tag to operate ina timed powered up synchronized listening mode for a predefinedsynchronized tag listening time during which the RFID tag activelylistens for transmitted first band RF signal interrogator pollingsignals, performing the following steps if an interrogator pollingsignal is received during a given synchronized listening mode:processing the latest received interrogator polling signal, performingone or more tag processing operations, increasing or decreasing thelength of the predefined synchronized sleep time based on the givenreceipt time of the interrogator polling signal as necessary to maintaina predefined alignment time between the start time of the synchronizedlistening mode and the given receipt time of the periodic interrogatorpolling signal, and then returning the RFID tag to the timedsynchronized low power sleep mode for the predefined synchronized sleeptime, and performing the following steps if an interrogator pollingsignal is not received during a given synchronized listening mode:decreasing the length of the predefined synchronized sleep time by anincremental amount of time, performing one or more tag processingoperations, and then returning the RFID tag to the timed synchronizedlow power sleep mode for the predefined synchronized sleep time if thenumber of consecutive times that an interrogator polling signal has notbeen received is less than a predefined threshold, or then operating theRFID tag in the non-synchronized state if the number of consecutivetimes that an interrogator polling signal has not been received isgreater than a predefined threshold.

In another respect, disclosed herien is a frequency identification(RFID) tag system, including: first band receiver or transceivercircuitry configured to receive periodic first band RF signalinterrogator polling signals and second band transmitter circuitryconfigured to transmit second band RF signal response signals inresponse thereto, the first band being a multiple channel-basedfrequency band and the second band being a non-channel based frequencyband; and at least one processing device to repeatedly and alternatelyoperate the RFID tag between a non-synchronized state with a periodicinterrogator polling signal and a synchronized state with a periodicinterrogator polling signal. In the non-synchronized state the at leastone processing device may be configured to: operate the first bandreceiver or transceiver circuitry of the RFID tag in a timednon-synchronized low power sleep mode for a predefined non-synchronizedsleep time during which the first band receiver or transceiver circuitrydoes not listen for transmitted first band RF signal interrogatorpolling signals, then wake up the first band receiver or transceivercircuitry to perform one or more tag processing operations, then returnthe first band receiver or transceiver circuitry to the timednon-synchronized low power sleep mode for the predefinednon-synchronized sleep time if the number of immediately previousconsecutive sleep times is less than a predefined threshold, or operatethe first band receiver or transceiver circuitry in a timed powered upnon-synchronized listening mode for a predefined non-synchronized taglistening time during which the first band receiver or transceivercircuitry actively listens for transmitted first band RF signalinterrogator polling signals if the number of immediately previousconsecutive sleep times is greater than or equal to a predefinedthreshold. In the synchronized state the at least one processing devicemay be configured to: operate the first band receiver or transceivercircuitry in a timed synchronized low power sleep mode for a predefinedsynchronized sleep time during which the first band receiver ortransceiver circuitry does not listen for transmitted first band RFsignal interrogator polling signals, then wake the first band receiveror transceiver circuitry to operate in a timed powered up synchronizedlistening mode for a predefined synchronized tag listening time duringwhich the first band receiver or transceiver circuitry actively listensfor transmitted first band RF signal interrogator polling signals,perform the following steps if an interrogator polling signal isreceived during a given synchronized listening mode: process the latestreceived interrogator polling signal, perform one or more tag processingoperations and increase or decrease the length of the predefinedsynchronized sleep time based on the given receipt time of theinterrogator polling signal as necessary to maintain a predefinedalignment time between the start time of the synchronized listening modeand the given receipt time of the periodic interrogator polling signal,and then return the RFID tag to the timed synchronized low power sleepmode for the predefined synchronized sleep time, and perform thefollowing steps if an interrogator polling signal is not received duringa given synchronized listening mode: decrease the length of thepredefined synchronized sleep time by an incremental amount of time andperform one or more tag processing operations, and then return circuitryof the RFID tag to the timed synchronized low power sleep mode for thepredefined synchronized sleep time if the number of consecutive timesthat an interrogator polling signal has not been received is less than apredefined threshold, or then operate the RFID tag in thenon-synchronized state if the number of consecutive times that aninterrogator polling signal has not been received is greater than apredefined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an aRFID communication system according to one exemplaryembodiment of the disclosed systems and methods.

FIG. 2 is a block diagram of an aRFIDI system according to one exemplaryembodiment of the disclosed systems and methods.

FIG. 3 is a block diagram of an interrogator daughtercard according toone exemplary embodiment of the disclosed systems and methods.

FIG. 4 is a block diagram of circuitry for a multi-band aRFID tagaccording to one exemplary embodiment of the disclosed systems andmethods.

FIG. 5 is a statechart illustrating methodology according to oneexemplary embodiment of the disclosed systems and methods.

FIG. 6 is a block diagram of a UWB processing system according oneexemplary embodiment of the disclosed systems and methods.

FIG. 7 shows an aRFID communication system according to one exemplaryembodiment of the disclosed systems and methods.

FIG. 8 is a block diagram of UWB data processing network systemaccording to one exemplary embodiment of the disclosed systems andmethods.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 illustrates one exemplary embodiment of an aRFID communicationsystem 100 that includes a master coverage area 194 defined betweenouter boundary 102 and inner boundary 104 of the system 100. In oneembodiment such a master coverage area may be, for example 1 mile by 1mile square, although other sized master coverage areas (both smallerand larger), and/or other shapes of master coverage areas may beimplemented in other embodiments. Although an aRFID system andassociated devices are described herein, it will be understood thatembodiments of the disclosed systems and methods may also be implementedwith passive RFID tags and semi-passive RFID tags, as well as RFIDcommunication systems employing the same.

As shown in FIG. 1, a remote active RFID interrogator (aRFIDI) system190 with its corresponding directional signal transmission system (e.g.,multiple outwardly facing antenna panels) is positioned within theboundaries of (e.g., in this case substantially at the center of) themaster coverage area 194 (e.g., on an elevated tower). In thisembodiment, the directional signal transmission system includes anantenna array of eight outwardly-facing 45° beamwidth transmissionantenna panels 108 that are equally spaced such that they together covera full 360 degrees of transmission angle as shown, i.e., allowing theselective scanning of eight 45° sector coverage areas 110, 112, 114,116, 118, 120, 122 and 124 one sector coverage area at a time. However,it will be understood that in other embodiments a directional signaltransmission system need not be positioned near the center of a mastercoverage area, or even within the boundaries of a master coverage area,e.g., a directional signal transmission system may be positioned on ornear a boundary of a master coverage area, and/or cover less than a full360 degrees of transmission angle. Further, more than one aRFIDI system190 may be positioned within a common master coverage area, and/oradditional aRFIDI systems 190 may be added over time, e.g., as thenumber of aRFID tags 180 within a master coverage area grows.

Still referring to FIG. 1, the aRFIDI system 190 also includes NBFMinterrogator transmitter circuitry 106 that is coupled to each of theeight 45 degree antenna panels 108. In one exemplary embodiment, theaRFIDI system 190 may be configured for transmission using NBFM signaltransmissions in an unlicensed 900 MHz frequency band (ranging from902-907 MHz) or an unlicensed 915 MHz ISM band (ranging from 902-928MHz) or unlicensed 433 MHz frequency band or any other unlicensed band,it being understood that other unlicensed or licensed frequency bandsand non-NBFM frequencies may alternatively be employed for interrogatorfirst band transmissions depending on the area of use and/or needs ofthe given application. In one exemplary embodiment, aRFIDI interrogatorsystem 190 may include NBFM interrogator transmitter circuitry 106 thatis coupled to and controlled by at least one processing device, e.g.,microprocessor, central processing unit (CPU), field gate programmablearray (FPGA), application specific integrated circuit (ASIC), etc.

In one exemplary embodiment, outer boundary 102 and inner boundary 104of aRFID communication system 100 may be, for example, fence lines of acattle feedlot, although outer boundary 102 and inner boundary 104 ofaRFID communication system 100 may alternatively represent other typesof master coverage areas 194, e.g., such as walls of a prison yard,inner and outer boundary walls of a race track, walls of a warehousebuilding, etc. Size of master coverage area 194 may vary, depending onthe needs of a given application, but in one embodiment size of asquare-shaped master coverage area 194 may be from about 1 to about 4miles across (e.g., from about 640 acres to about 10,240 acres in arealcoverage). It will also be understood that the particular outer boundary102 and inner boundary 104 of aRFID communication system 100 areexemplary only, and other shapes and sizes of master coverage areas 194may be implemented in the practice of the disclosed systems and methods.Moreover, boundaries 102 and 104 need not be present as physicalboundaries, e.g., interrogator system 190 may be positioned on anelevated tower in the center of feedlot with no physical boundary aroundthe tower. In addition it is not necessary that an aRFIDI system bepositioned in the center of a master coverage area as is the case in theexemplary embodiment of FIG. 1.

Still referring to FIG. 1, individual roaming aRFID tags 180 are showndynamically changing position within master coverage area 194. Dependingon the given application, each of aRFID tags 180 may be attached orotherwise associated with a carrier, such as an animal, person orvehicle. In the exemplary embodiment of FIG. 1, roaming aRFID tags 180are randomly moving within master coverage area 194, such as would bethe case with cattle moving within a feed lot, or boxes in a warehouse.In other embodiments, such as would be the case with a race track,individual tags may be moving in a common direction around the course ofthe track.

In one exemplary embodiment, each of aRFID tags 180 may be configuredwith the capability to receive NBFM transmissions in one of at least 50NBFM channels that are randomly distributed among the aRFID tags 180with a channel spacing of about 100 KHz. For example, when each aRFIDtag is programmed, one of fifty 900 MHz channels may be selected as thattag's default frequency, so that the manufactured tags are evenlydistributed among the 50 available channels. In this regard, 50 channelsis the current minimum number of channels required to meet FCCrestrictions for a frequency hopping system within the 900 MHZ ISM band(902-928 MHz). Operation under the FCC frequency hopping definitionenables a maximum amount of power to be transmitted (+36 dBm), whichincreases the overall range of the aRFIDI system 100 in one exemplaryembodiment to approximately 4 miles. However, it will be understood thatany other number of multiple interrogation channels (e.g., greater orlesser than 50 channels) may be employed in the practice of thedisclosed systems and methods.

During operation, aRFIDI system 190 selectively scans the eight 45°sector coverage areas 110, 112, 114, 116, 118, 120, 122 and 124 one at atime and in succession in order to spatially separate the mastercoverage area into eight parts, i.e., so that aRFIDI system 190 onlytransmits interrogator polling signals to one sector coverage area at atime. To scan each sector coverage area, the aRFIDI system 190 transmitsa data packet (e.g., at 19.2K baud data rate) on a first one of the 50NBFM channels for a given transmit time (e.g., of about 2.5 ms) followedby an additional pause time that may optionally be greater than thegiven transmit time (e.g., to yield a total dwell time for each channelthat is about 20 ms) before changing over to the next one of the 50 NBFMchannels in a frequency hopping manner. In this way, the aRFIDI system190 may be configured to frequency separate the tags present within amaster coverage area by transmitting once on each of the 50 channels(e.g., for a total dwell of 1 second) in each of the 8 sector coverageareas (e.g., yielding a revisit time of 8 seconds). As will be describedfurther herein, each of the given RFID tags 180 that are present in thecurrent sector coverage area (and which are configured to receive on thecurrent specifically broadcast NBFM channel) will respond on a secondand different band from the NBFM band with a transmission (e.g., UWBtransmission) of their own upon receiving the current NBFM interrogationsignal on their specific assigned channel.

Second band receiver antennas 160 of FIG. 1 are positioned as shown atknown locations at the corners of outer boundary 102 to receive the tagsecond band transmissions for further processing, e.g., tracking,localization and/or transmittal of information. In this embodiment, eachof tags 180 is configured not to transmit a UWB signal (e.g., when it isset to interrogate or standby mode) unless a specially formattedinterrogate data packet is received by the given tag at 19.2 k baud, onits factory pre-programmed NBFM channel. When employed as a second bandsignal in this exemplary embodiment, a UWB signal is an antennatransmission in the range of 3.1 GHz up to 10.6 GHz at a limitedtransmit power of −41.3 dBm/MHz with an emitted signal bandwidth thatexceeds the lesser of 500 MHz or 20% of the center frequency. In thisembodiment UWB signals are employed for second band signalcommunication. However, it will be understood that other non-UWBcommunication signals (e.g., signals of other non-multiple channel-basedfrequency band) may be employed for second band communication in thepractice of the disclosed systems and methods depending on the area ofuse and/or needs of the given application (e.g., 433 MHz or 915 MHzfrequency bands or other suitable band). Moreover, it is also possiblethat more than two bands may be employed for communication by an aRFIDcommunication system 100.

For a square-shaped master coverage area 194 having side dimensions ofabout 1 mile in length, receivers 160 are spaced about 0.7 miles fromthe transmission antenna panels 108 of the centrally located aRFIDIsystem 190, and for a square-shaped master coverage area 194 having sidedimensions of about 4 miles in length, receivers 160 are spaced about2.8 miles from the transmission antenna panels 108 of the centrallylocated aRFIDI system 190. However, it will be understood thatantenna/receiver spacing may vary according to the specific mastercoverage area dimensions of a given aRFID communication system 100,and/or with the transmission and reception capabilities of a given aRFIDcommunication system 100. Further, it will be understood that in thosecases where the first band signal communication range of an aRFIDIsystem 190 will not reach the entire area of its corresponding mastercoverage area 194, those aRFID tags 180 that are located outside thefirst band signal communication range of any aRFIDI system 190 may beconfigured to intermittently transmit second band response signals,e.g., in a manner as described and illustrated in relation to step 556of the non-synchronized state 570 of FIG. 5 described further herein.

Thus, in the illustrated exemplary embodiment of FIG. 1, aRFIDI system190 combines spatial (time-separated spaces) and frequency separation(frequency hopping) techniques in order to reduce the tag density by afactor of 400 (i.e., 8 sectors×50 channels per sector) in any one secondinterval. However, it will be understood that in other embodiments, thateither of such spatial or frequency separation techniques may bepracticed alone without the other. Furthermore, it will also beunderstood that code division multiple access (“CDMA”) and/or frequencydivision multiple access (“FDMA”) may be implemented as channel accessmethods in combination with the spatial (time-separated spaces) andfrequency separation (frequency hopping) techniques employed herein.

One exemplary embodiment of 50 possible 900 MHz frequencies that may beemployed by aRFIDI system 190 for channels 1-50 is shown in thefollowing Table 1.

TABLE 1 Exemplary Interrogator and Tag 900 MHz Frequency ChannelsChannel # Freq. 1 902.0 2 902.1 3 902.2 4 902.3 5 902.4 6 902.5 7 902.68 902.7 9 902.8 10 902.9 11 903.0 12 903.1 13 903.2 14 903.3 15 903.4 16903.5 17 903.6 18 903.7 19 903.8 20 903.9 21 904.0 22 904.1 23 904.2 24904.3 25 904.4 26 904.5 27 904.6 28 904.7 29 904.8 30 904.9 31 905.0 32905.1 33 905.2 34 905.3 35 905.4 36 905.5 37 905.6 38 905.7 39 905.8 40905.9 41 906.0 42 906.1 43 906.2 44 906.3 45 906.4 46 906.5 47 906.6 48906.7 49 906.8 50 906.9

FIG. 2 is a simplified block diagram of an aRFIDI system 190 of FIG. 1as it may be configured according to one exemplary embodiment of thedisclosed systems and methods. As shown in FIG. 2, aRFIDI system 190 mayinclude a interrogator host card 200 (e.g., printed circuit board) thatis provided with eight interrogator daughtercards 204 coupled to a hostmicroprocessor 202 by a serial peripheral interface (SPI) bus or othersuitable signal communication bus. Host microprocessor 202 may be, forexample, a RCM3000 RabbitCore® 10 Base-T Ethernet microprocessor coremodule with program memory that is available from Rabbit SemiconductorInc. of Davis, Calif., or other suitable processing device (e.g.,microprocessor, processor, field programmable gate array, applicationspecific integrated circuit, etc.). In this embodiment, hostmicroprocessor 202 is also coupled to each daughtercard 204 by adaughtercard interrupt line 208 and a daughtercard power amplifiercontrol line 210. Each of daughtercards 204 is in turn coupled to arespective antenna (panel) 108, e.g., 45° beamwidth transmission antennapanels that are equally spaced such that they together cover a full 360degrees of transmission angle as previously described in relation toFIG. 1. As further shown, host microprocessor 202 may include anEthernet connection 295 to provide a network connection to aRFIDI system190, e.g., for receiving commands at the host processor 202 from aremote application over a network.

FIG. 3 is a simplified block diagram of an interrogator daughtercard 204of FIG. 2 which may be, for example, a printed circuit board. As shown,each daughtercard 204 includes narrow band transmitter circuitry 302coupled to RF power amplifier circuitry 304 through RF balun 306.Narrowband transmitter circuitry 302 may be, for example, a CC1101 sub-1GHz RF transceiver available from Texas Instruments of Dallas, Tex., oranother suitable narrowband RF transceiver or transmitter. RF poweramplifier circuitry 304 may be, for example, a MAX2232 low voltage 900MHz ISM silicon power amplifier available from Maxim IntegratedProducts, Inc. of Sunnyvale Calif., or other power amplifier suitablefor 900 MHz ISM transmissions. Further shown in FIG. 3 are optionalindicator light emitting diodes 308 that may be present to indicateinterrogator daughterboard operating parameter states such as main poweron/off state, RF transmission on/off state, power amplifier on/offstate, etc. It will be understood that an aRFIDI system 190 may beoptionally provided with receive capability in one exemplary embodiment,e.g., by providing each daughterboard 204 with a narrowband transceiveror a combination of narrowband transmitter and receiver components. Sucha receive capability may be provided, for example, to allow aRFIDIsystem 190 to receive data such as relayed sensor data or other storedinformation that is transmitted by a RFID tag 180 via first band RFsignal communications.

During operation, host microprocessor 202 of host card 200 controlscomponents of a first daughterboard 204 corresponding to a first sectorcoverage area to transmit interrogator polling signals (e.g., speciallyformatted data packets at 19.2K baud data rate) on each of the multiple(e.g., 50) NBFM channels within the first sector coverage area, followedby controlling components of a second daughterboard 204 corresponding toa second sector coverage area to transmit interrogator polling signalson each of the multiple NBFM channels within the second sector coveragearea, and so on in sequential fashion until each of the eightdaughterboards 204 has so transmitted on each of the multiple NBFMchannels within its corresponding sector coverage area, at which timethe process is repeated starting again with the first daughterboard 204.

To control components of each respective daughterboard 204 to transmitinterrogator signals at the desired time, host microprocessor 202communicates outgoing data packets to the narrowband transmitter 302 ofthe respective daughterboard 204 by way of SPI bus 206. The narrowbandtransmitter 302 signals the completion of packet transmission to thehost microprocessor 202 via an interrupt line 208. Host microprocessor202 toggles the RF Power Amplifier on and off by way of PA control line210. During operation, the indicator LED's 308 may be activated toindicate when the respective daughterboard 203 is powered up, when therespective daughterboard 204 is transmitting RF signals, and when thepower amplifier 304 of the respective daughterboard 204 is powered up.

Other optional functions that may be performed by host microprocessor202 of host card 200 include tag management tasks which may beimplemented to enable aRFIDI system 190 to keep track of individualaRFID tags 180 or groups of aRFID tags 180 (i.e., if aRFIDI system 190is configured with optional receive capability), and/or to changeconfiguration parameters of one or more aRFID tags 180. For example,host microprocessor 202 may control aRFIDI system 190 to send commandsby NBFM signals to one or more aRFID tags 180 that are operable tochange one or more operations of the aRFID tag 180 (e.g., such as datareport rate, transmit power levels, tag sleep intervals, etc.), e.g.,based on a request received at network connection 295 from a remoteapplication over a connected network). In this regard, it is possiblethat a NBFM command signal may be broadcast to only change operation ofan individual aRFID tag 180, or that a NBFM command signal may bebroadcast instructing all aRFID tags 180 within range of aRFIDI system190 to change their operation.

FIG. 4 illustrates one exemplary embodiment of circuitry 400 formulti-band aRFID tag 180 such as may be employed in the aRFIDcommunication system 100 of FIG. 1. As shown in FIG. 4, aRFID tag 180includes an NBFM antenna element 402 for receiving NBFM interrogatorpolling signals from aRFIDI system 190 of FIG. 1, and may optionallyreceive NBFM data transmissions from one or more local or embeddedsensors (e.g., that report data about the object to which aRFID tag 180is associated with or the local environment) or other equipment. NBFMantenna element 402 is coupled as shown to NBFM transceiver circuitry406 that receives and transmits analog NBFM signals from NBFM antennaelement 402 and exchanges digital NBFM signals with tag microcontroller410. NBFM transceiver circuitry 406 may also operate to optionallytransmit command signals to one or more sensors, change data rates orinformation content, etc. A tag battery or battery pack 450 may also beprovided for aRFID tag 180 as shown, to provide power for operation ofother components of aRFID tag 180 including tag microcontroller 410,NBFM transceiver circuitry 406, and UWB transmitter circuitry 412. Inone exemplary embodiment, components of aRFID tag 180 may behermetically sealed and isolated from the outside environment with noexternally accessible electrical interconnections, i.e., such that thetag is only capable of wireless communication.

Still referring to FIG. 4, tag microcontroller 410 processes receivedNBFM interrogator polling signals (e.g., to determine if the receivedsignal is of the correct data packet format corresponding to aninterrogator polling signal transmitted by aRFIDI system 190), and inresponse thereto controls operation of UWB transmitter circuitry 412 toproduce and transmit a UWB response signal via coupled UWB antennaelement 404 that is formatted to include tag identification informationthat is unique to the given aRFID tag 180. A UWB response signal mayalso include status information about the tag, data points from optionalsensor circuitry that may be associated with or in communication withthe tag, etc. Tag microcontroller 410 may also optionally preprocessreceived sensor data prior to relaying this data to receiver circuitrycoupled to each of UWB receiver antennas 160, and/or may also optionallyprovide power control signals to each of NBFM transceiver circuitry 406and UWB transmitter circuitry 412 (e.g., in order to conserve powerconsumed by these components of aRFID tag 180 in-between tagtransmissions). It will be understood that an interrogator pollingsignal may also include other instructions to control operations ofaRFID tag 180, e.g., to cause aRFID tag 180 to record data from one ormore external sensors, to cause aRFID tag 180 to transmit or otherwiseexchange NBFM RF signals with other devices, to cause aRFID tag 180 toalter its timed sleep and listening cycles, etc.

As further shown in FIG. 4, tag microprocessor circuitry 410 may becoupled to on board data storage circuitry 416 (e.g., non-volatilememory), which may be provided for storage of records about theobject/inventory being tracked or monitored, e.g., tag location datapoints giving history of where the object/inventory has been, UWB andNBFM data packet format information, data from optional circuitry (e.g.,such as sensor circuitry that monitors one or more parameters of theenvironment in which the aRFID tag 180 exists at a given time),object/inventory ownership or identification information, medical orvaccination records (e.g., where the object is a cow or otherlivestock), etc. Further examples of possible functions and circuitrythat maybe incorporated within a RFID tag 180, as well as collection andreporting of sensor data using such a RFID tag, may be found inconcurrently filed U.S. patent application Ser. No. ______, entitled“SYSTEMS AND METHODS FOR RFID TAG OPERATION” by Scott M. Burkart, et.al., which is filed on the same date as the present application andwhich is incorporated herein by reference in its entirety. Examples ofsuitable UWB transmitter circuitry and UWB methodology that may beemployed for UWB transmissions between aRFID tag 180 and aRFIDI system190 include, for example, transmitter circuitry described inconcurrently filed U.S. patent application Ser. No. ______, entitled“SYSTEMS AND METHODS FOR GENERATING PULSED OUTPUT SIGNALS USING A GATEDRF OSCILLATOR CIRCUIT” by Ross A. McClain Jr., et al., and signaltransmission systems and methods described in concurrently filed U.S.patent application Ser. No. ______, entitled “PULSE LEVEL INTERLEAVINGFOR UWB SYSTEMS,” by Bryan L. Westcott, et al., each of which is filedon the same date as the present application and each of which isincorporated herein by reference in its entirety.

Still referring to FIG. 4, tag microcontroller 410 may be configured inone exemplary embodiment to maintain synchronization with NBFMinterrogator polling signals from aRFIDI system 190 within a sectorcoverage area. For example, components of an aRFID tag 180 may beconfigured to perform the tag active operations (e.g., data processing,UWB response signal transmission, gathering data from sensors, etc.)after receiving a polling signal from aRFIDI system 190, and then toenter a timed low power sleep mode to reduce power consumptionin-between interrogator polling signals from system 190. Tagmicrocontroller 410 may be programmed with a sleep timer that wakes upthe components of aRFID tag 180 before the next polling packet of anNBFM interrogator polling signal arrives from aRFIDI system 190. Due torelatively high power consumption rate of NBFM transceiver 406, thecloser in time that the components of aRFID tag 180 (including NBFMtransceiver 406) awake before receipt of the next polling packet, themore power that may be conserved to increase tag battery life. Such aconfiguration allows aRFID tag 180 to operate with a very small receivebuffer time while staying synchronized with aRFIDI system 190.

Further shown in FIG. 4 is an optional tag external indicator 490 whichmay be provided onboard an aRFID tag 180. Tag external indicator 490 maybe, for example, a visual indicator (e.g., light emitting diode, smallstrobe light, etc.), motion based indicator (e.g., vibrator), and/or anaudio indicator (e.g., small speaker or beeper, etc.) that is powered bybattery 450 and controlled by tag microcontroller 210. When present,such an optional tag external indicator 490 may be remotely activated bymicrocontroller 410 in response to an indicator request, for example,sent by first band NBFM signal transmissions to aRFID tag 180 from a taginterface device. When activated, external indicator 490 may be employedto produce an external indication (e.g., noise, light, motion such asvibrations, etc.) externally alert those persons in visual and/oraudible range of indicator 490 of the current location of aRFID tag 180and/or of a particular status of aRFID tag 180 or of an object withwhich it is associated.

Examples of suitable UWB transmitter circuitry and UWB methodology thatmay be employed for UWB transmissions between aRFID tag 180 and aRFIDIsystem 190 include, for example, transmitter circuitry described inconcurrently filed U.S. patent application Ser. No. ______, entitled“SYSTEMS AND METHODS FOR GENERATING PULSED OUTPUT SIGNALS USING A GATEDRF OSCILLATOR CIRCUIT” by Ross A. McClain Jr., et al., and signaltransmission systems and methods described in concurrently filed U.S.patent application Ser. No. ______, entitled “PULSE LEVEL INTERLEAVINGFOR UWB SYSTEMS,” by Bryan L. Westcott, et al., each of which is filedon the same date as the present application and each of which isincorporated herein by reference in its entirety. Further information onmethodology that may be employed for communication using RFID tags 180may be found in concurrently filed U.S. patent application Ser. No.______, entitled “MOBILE COMMUNICATION DEVICE AND COMMUNICATION METHOD,”by Bryan L. Westcott et al., which is filed on the same date as thepresent application and which is incorporated herein by reference in itsentirety.

FIG. 5 is a statechart diagram that illustrates one exemplary embodimentof methodology 550 that may be employed to keep an aRFID tag 180 insynchronization (while minimizing tag power consumption) with an aRFIDIsystem 190 such as found in aRFID communication system 100 illustratedand described herein. In methodology 550 of FIG. 5, an aRFID tag 180initially starts out in a non-synchronized (“Not Synced”) state 570(i.e., aRFID tag 180 is not in synchronization with aRFIDI system 190).In this non-synchronized state 570, aRFID tag 180 attempts to receiveits first NBFM interrogator (polling) packet from aRFIDI system 190 instep 552, where it listens for a NBFM polling packet for a predefinednon-synchronized tag listening time “Nbfm_timeout” set when enteringstep 552. In one exemplary embodiment, tag listening time may be set tobe 8 seconds or other predefined time period that corresponds to thetotal polling time or revisit rate of an associated aRFIDI system toensure that opportunity is given for aRFID tag 180 to be listening instep 552 at the same time the aRFIDI system transmits a NBFM pollingpacket. In this regard, a total polling time of aRFIDI system 190 ofFIG. 1 may be 8 seconds in one exemplary embodiment, with one secondbeing allocated to consecutively scan each of eight 45° sector coverageareas 110, 112, 114, 116, 118, 120, 122 and 124 as previously describedherein. However, a tag listening time may be set to any other value thatis desired or needed to fit the characteristics of a given applicationand/or aRFIDI system/s.

If a NBFM polling packet is found to be received in conditional step553, then aRFID tag 180 now enters a synchronized state 580 with aRFIDIsystem 190 and goes to step 560 where methodology 500 proceeds in amanner that will be described further below. On the other hand, if inconditional step 553 no polling packet is found received during thepredefined “Timeout” listening time of step 552, then aRFID tag 180proceeds to step 554 where aRFID tag 180 enters a timed low power sleepmode (during which NBFM transceiver circuitry 406 remains off) and setsan non-synchronized sleep timer “SetSleepTime” so that aRFID tag 180sleeps for a predefined time that may also correspond to the pollingrate of aRFIDI system 190 (e.g., 8 seconds in this example). At the sametime step 554 is entered, a counter is set to equal a predefined maximumnumber of consecutive sleep cycles (e.g., 450 sleep cycles or otherpredefined number of sleep cycles). Such a non-synchronized state 570may exist, for example, when aRFID tag 180 is not within range of aninterrogator system 190, when an interrogator system 190 is not active(e.g., such as when undergoing maintenance or due to power failure), ordue to transmission problems such as lost packets, multi-path problems,etc. In such a case, 450 sleep cycles at 8 seconds per sleep cycle wouldyield a total time of 3600 seconds or one hour down time betweenrequired NBFM transceiver power up intervals for listening in step 552,resulting in reduced power consumption while aRFID tag 180 is in anon-synchronized state with an interrogator system 190, while at thesame time allowing normal tag processing operations to be carried out.

Still referring to FIG. 5, once aRFID tag 180 proceeds tonon-synchronized sleep timer of step 554, aRFID tag 180 goes into lowpower sleep mode and continues to wake every predefined time period(e.g., 8 seconds) to function independently (i.e., withoutsynchronization with aRFIDI system 190) by moving from step 554 to step556 and performing tag processing operations in step 556 (e.g., dataprocessing, UWB response signal transmission, gathering data fromsensors, etc.) before returning through conditional step 557 to step 554to sleep for another predefined time, and then waking up again toproceed to step 556 for tag processing operations again. In conditionalstep 557, the value of the maximum sleep cycle counter is evaluated todetermine if it is less than or equal to zero. In this regard, themaximum sleep cycle counter is decremented by an amount of one each timeaRFID tag 180 exits step 554 so that after cycling between steps 554,556 and 557 for the predefined maximum number of sleep cycles, themaximum sleep cycle counter value becomes equal to zero. During the timethat aRFID tag 180 cycles between steps 554, 556 and 557 innon-synchronized state 570 with a maximum sleep counter value greaterthan zero in step 557, no attempt is made to listen for NBFM pollingpackets and NBFM transceiver circuitry 406 remains off, thus savingpower consumption. But when the maximum sleep cycle counter is found tobe equal to a value less than or equal to zero in step 557, the“Nbfm_timeout” is set again to 8 seconds and methodology 550 returns tolisten step 552 where NBFM transceiver circuitry 406 is activated for ashort period of time and another attempt is again made to receive afirst NBFM polling packet from aRFIDI system 190. The steps ofnon-synchronized state 570 are then repeated as before.

Once a NBFM polling packet is found to have been received by aRFID tag180 in conditional step 553 of FIG. 5, then aRFID tag 180 enters asynchronized (“Synced) state 580 with aRFIDI system 190 and proceeds tostep 560 as shown. At the same time, a synchronized sleep timer“SleepTime” is set to a predefined sleep time based on receivedinterrogator packet timing as will be described further below and amissed packets counter “missedPkts” is initially set to equal zero. Instep 560, aRFID tag 180 enters a timed low power sleep mode and sleepsfor the predefined synchronized sleep time that in one exemplaryembodiment may correspond to 8 seconds minus a receive buffer (typically2 milliseconds) minus the time since receipt of the last interrogatepacket (the time used for other tag functions, e.g., typically a fewmilliseconds) resulting in a set sleep time of slightly less than 8 sseconds in this exemplary embodiment. After entering the low power sleepmode, aRFID tag 180 will wake after the set synchronized sleep time andlisten in step 562 for NBFM polling packets for a predefinedsynchronized time “Nbfm_timeout” (e.g., 10 milliseconds or otherpredefined time period).

In most cases, aRFID tag 180 will receive a polling packet in listeningmode step 562 within a short receive buffer time (e.g., from about 2 toabout 3 milliseconds). Assuming aRFID tag 180 successfully receives aNBFM polling packet from aRFIDI system 190 as expected, the missedpacket counter “missedPkts” is set to zero and aRFID tag 180 processesthe received NBFM polling packet in step 564 (e.g., completing tasks asrequested by the interrogator, including sending out UWB packets,activating tag LED, changing data rates, etc.). At the same time, thesleep timer may be dynamically adjusted in real time (e.g., increased ordecreased) again based on received packet timing (e.g., by refining thesleep time used in order to maintain the desired receive buffer time ofabout 2 milliseconds; this refining may be based on the actual timebetween when the tag wakes and the receipt of an interrogator packet).Then aRFID tag 180 continues with whatever tag processing operations arenecessary in step 566 (e.g., data processing, UWB response signaltransmission, gathering data from sensors, etc.). After the tagprocessing operations are complete, aRFID tag 180 returns as shown tostep 560, where aRFID tag 180 once again enters the timed low powersleep mode and sleeps for the predefined synchronized sleep time in themanner previously described.

However, if a NBFM polling packet is not received in step 562 before the“Nbfm_timeout” value is reached, then the aRFID tag 180 increments thepacket missed counter “missedPkts” by one, and the synchronized sleeptime is dynamically decreased in real time (e.g., slightly by about 3milliseconds). This adjustment may be made to cover the event that aRFIDtag 180 woke just after transmission of the NBFM interrogator (polling)packet. Methodology 550 then proceeds to conditional step 568 where thevalue of the missed packet counter “missed_pkts” is evaluated to see ifit meets or exceeds a predefined threshold value of missed packets(e.g., five missed packets or other predefined number of missedpackets). If the value of the “missed_pkts” counter is found in step 568not to meet or exceed the predefined threshold number of missed packets,then aRFID tag 180 proceeds to tag processing operations of step 566(e.g., data processing, UWB response signal transmission, gathering datafrom sensors, etc.) in a manner as previously described. However, if instep 568 the value of the “missed_pkts” counter is found to meet orexceed the predefined threshold number of missed packets, then it isassumed that aRFID tag 180 has lost synchronization with aRFIDI system190, and aRFID tag 180 returns to non-synchronized state 570 where itenters step 552 and listens for a NBFM interrogator (polling) packet ina manner as previously described herein.

Returning now to FIG. 1, each of UWB receiver antennas 160 areconfigured to receive the UWB response signal transmissions from each ofaRFID tags 180, and are coupled to provide the received signals and timeof UWB response signal reception at each antenna 160 to a dataprocessing system (e.g., UWB processing system 500 in this exemplaryembodiment) for signal processing tasks such as tag tracking,localization and/or decoding of information (e.g., monitoredenvironmental or object information from sensor circuitry) transmittedfrom a given aRFID tag 180 in a UWB response signal.

FIG. 6 illustrates one exemplary embodiment of a UWB processing system500 that may be coupled to the four UWB receiver antennas 160 of knownlocation that were previously illustrated and described in relation toFIG. 1. It will be understood that although four or more UWB receiverantennas 160 may be employed to determine the three-dimensional positionof a transmitting aRFID by multilateration or hyperbolic positioning,fewer than four UWB receiver antennas 160 may be alternatively employedin other embodiments where three dimensional location determination isnot required. Thus, three UWB receiver antennas 160 may be employed toallow two-dimensional determination of the location of a giventransmitting aRFID tag 180 based on time difference of arrival (TDOA)methodology. In other embodiments, one or two UWB receiver antennas 160maybe employed, e.g., where only transmitting information from an aRFIDtag 180 via UWB communications and/or where aRFID tag location isdetermined based only partially on the TDOA between two UWB receiverantennas 160.

Still referring to FIG. 6, each of UWB receivers 502 has a system clock505 that is synchronized with the one pulse per second output from anassociated GPS receiver, although a local clock may be employed in otherembodiments (e.g., atomic clock, or local clock that is synchronizedwith system clocks of other UWB receivers 502 using any suitablesynchronization methodology). As so configured, each receiver canmaintain its own highly accurate clock for time tagging of the receivedUWB signal. The time of receipt of a given UWB response signaltransmission 510 from a given aRFID tag 180 at each of the fourdifferent UWB receivers 502 is measured by the synchronized system clock505 of each receiver 502 and communicated via digital receiver datasignal 512 (along with any sensor data or other information contained inthe UWB response signal) to UWB processing circuitry 504 of UWBprocessing system 500. UWB processing system 500 may be, for example, amicroprocessor or other type of processing device/s that is suitable forperforming time difference of arrival (TDOA) calculations and/or otherprocessing tasks on the UWB response signal (and information containedtherein) that is received by UWB receivers 502. Assuming that the givenaRFID tag 180 (i.e., that is transmitting the given UWB response signal)is not located at an unfavorable geometry from each of the four UWBantennas 160, then there will be difference in time of arrival of theUWB response signal at each UWB receiver 160 relative to each other. UWBprocessing circuitry 504 may be configured to calculate the currentthree-dimensional location in x,y,z coordinates relative to the knownx,y,z coordinate locations of each of the four different UWB receivers502, and to output this calculation as digital processed tag information514 (e.g., tag location coordinates, collected and/or processed sensorinformation, etc.) for storage, display and/or further processing.

UWB processing circuitry 504 may calculate the current three-dimensionallocation of a transmitting aRFID tag 180 using any suitablemultilateration or hyperbolic positioning methodology. For example, inone exemplary embodiment, given a transmitting aRFID tag 180 at anunknown location (x_(t), y_(t), z_(t)) and four UWB receivers 502 atknown locations A, B, C and D (expressed coordinates as (X_(A), Y_(A),Z_(A)), (X_(B), Y_(B), Z_(B)), (X_(C), Y_(C), Z_(C)), and (X_(D), Y_(D),Z_(D))), the travel time (T) of pulses from an aRFID tag 180 located at(x,y,z) to each of the UWB receivers 502 is the distance divided by thepulse propagation rate (c) (e.g., speed of light) as follows:

$T_{A} = {\frac{1}{c}\left( \sqrt{\left( {x_{t} - x_{A}} \right)^{2} + \left( {y_{t} - y_{A}} \right)^{2} + \left( {z_{t} - z_{A}} \right)^{2}} \right)}$$T_{B} = {\frac{1}{c}\left( \sqrt{\left( {x_{t} - x_{B}} \right)^{2} + \left( {y_{t} - y_{B}} \right)^{2} + \left( {z_{t} - z_{B}} \right)^{2}} \right)}$$T_{C} = {\frac{1}{c}\left( \sqrt{\left( {x_{t} - x_{C}} \right)^{2} + \left( {y_{t} - y_{C}} \right)^{2} + \left( {z_{t} - z_{C}} \right)^{2}} \right)}$$T_{D} = {\frac{1}{c}\left( \sqrt{\left( {x_{t} - x_{D}} \right)^{2} + \left( {y_{t} - y_{D}} \right)^{2} + \left( {z_{t} - z_{D}} \right)^{2}} \right)}$

Taking the UWB receiver location D as the coordinate system origin,then:

$T_{D} = {\frac{1}{c}\left( \sqrt{x_{t}^{2} + y_{t}^{2} + z_{t}^{2}} \right)}$

and the TDOA between a UWB response signal arriving at UWB receiverlocation A and the other UWB receiver locations A, B & C is:

$\begin{matrix}{T_{A} = {T_{A} - T_{D}}} \\{= {\frac{1}{c}\left( {\sqrt{\left( {x_{t} - x_{A}} \right)^{2} + \left( {y_{t} - y_{A}} \right)^{2} + \left( {z_{t} - z_{A}} \right)^{2}} - \sqrt{x_{t}^{2} + y_{t}^{2} + z_{t}^{2}}} \right)}}\end{matrix}$ $\begin{matrix}{T_{B} = {T_{B} - T_{D}}} \\{= {\frac{1}{c}\left( {\sqrt{\left( {x_{t} - x_{B}} \right)^{2} + \left( {y_{t} - y_{B}} \right)^{2} + \left( {z_{t} - z_{B}} \right)^{2}} - \sqrt{x_{t}^{2} + y_{t}^{2} + z_{t}^{2}}} \right)}}\end{matrix}$ $\begin{matrix}{T_{C} = {T_{C} - T_{D}}} \\{= {\frac{1}{c}\left( {\sqrt{\left( {x_{t} - x_{C}} \right)^{2} + \left( {y_{t} - y_{C}} \right)^{2} + \left( {z_{t} - z_{C}} \right)^{2}} - \sqrt{x_{t}^{2} + y_{t}^{2} + z_{t}^{2}}} \right)}}\end{matrix}$

Each equation defines a separate hyperboloid, and the location of thetransmitting UWB receiver 160 (x_(t), y_(t), z_(t)) may be solved for inreal time.

In one exemplary embodiment, the unknown location of a transmitting RFIDtag 180 may be located (i.e., geolocated) using any suitable TDOAtechnique with the optional addition of a reference emitter that istransmitting at a known location in order to increase the accuracy ofthe location value determined using the selected TDOA technique, assistwith receiver clock calibration, etc.

In the practice of the disclosed systems and methods, the exemplaryaRFID communication system 100 of FIG. 1 may be successfully applied,for example, to a typical cattle feedlot scenario which has greater than100,000 tagged head of cattle roaming in a 2 square mile area. Such anaRFID tag density would be far out of reach of the capabilities ofconventional aRFID systems currently available today. However, byutilizing sector interrogation and receiver channelization, this aRFIDtag density scenario is manageable using the disclosed systems andmethods. In this regard, UWB receiver is capable of processing up to10,000 tag transmissions per second without any other additional densitymanagement means. With a standard update rate for a given tag set to 8seconds, a UWB receiver that is capable of processing 10,000 tagtransmissions per second is employed for such a 100,000 tag scenario.Thus, in one exemplary embodiment, the maximum achievable tag densityfor a UWB receiver is only limited by the number of tags transmitting onUWB during any one second time, which is then controlled by using theaRFIDI system 190.

FIG. 7 illustrates one alternative exemplary embodiment of an aRFIDcommunication system 700 having an aggregate coverage area 702 that ismade up of 25 smaller master coverage areas 194 that are each defined bymultiple aRFIDI systems 190 and a network of 36 UWB receiver antennas160 as shown. Each aRFIDI system 190 and its four adjacent UWB receiverantennas 160 of a given master coverage area 194 may operate to trackand otherwise communicate with aRFID tags 180 in a manner similar tothat described herein in relation to FIGS. 1-6. As shown, each mastercoverage area 194 of FIG. 7 shares a pair of UWB receiver antennas 160with at least one adjacent master coverage area 194, such that a givenUWB receiver antenna 160 may receive UWB broadcasts from aRFID, tags 180that are located in two or more adjacent master coverage areas 194. Eachof multiple UWB receiver antennas 160 may be coupled (e.g., via a datanetwork) to a common UWB processing system 500 that receives andprocesses all UWB response signal transmissions received from aRFID tags180 at any of multiple UWB receiver antennas 160 of aRFID communicationsystem 700, in a manner that will be described further in relation toFIG. 8.

Still referring to FIG. 7, although dotted lines are shown todifferentiate individual master cover areas 194, it will be understoodthat no physical boundaries may exist between each of the mastercoverage areas 194, e.g., so that individual aRFID tags 180 may freelyroam from one master coverage area 194 to another adjacent mastercoverage area 194 within aggregate coverage area 702. When implementingsuch an aggregate coverage area 702 using multiple smaller mastercoverage areas 194, it may be desirable to position individual aRFIDIsystems 190 of the master coverage areas 194 close enough together suchthat there is overlap in the NBFM polling transmission range betweenadjacent master coverage areas 194, i.e., to ensure that there are noNBFM polling “dead” spots within the aggregate coverage area 702.

It will be understood that individual aRFID tags may at some times bepositioned such that they are in first band signal communication rangeof more than one aRFIDI system 190 of the embodiment of FIG. 7 (e.g.,when located near a boundary between two adjacent master coverage areas194). In such a case, the methodology described and illustrated inrelation to FIG. 5 herein may be employed in one exemplary embodiment bysuch an individual aRFID tag 180 to keep it synchronized with a singleone of multiple aRFIDI systems 190 that may be in first band signalcommunication range with the given aRFIDI tag 180. In this regard, whenthe individual aRFID tag 180 first receives a NBFM polling packet fromone of multiple in-range aRFIDI systems 190, it uses the methodology ofFIG. 5 to enter a synchronized state 580 with that first given aRFIDIsystem 190 such that the aRFID tag 180 sleeps for a predefined time thatcorresponds to the polling rate of the first given aRFIDI system 190.Therefore, in this synchronized state, the given aRFID tag 180 does notreceive or act upon polling signals received from other in-range aRFIDIsystems 190 since the polling rates of adjacent aRFIDI systems 190 arenot synchronized with each other in this exemplary embodiment. If thegiven aRFID tag 180 loses signal communications with the first aRFIDIsystem 190 then it may resynchronize with another or second in-rangeaRFIDI system 190 using the methodology of FIG. 5.

One example of an application for such an aRFID communication system 700is a large cattle ranch where tagged cows or other types of taggedlivestock or wildlife may be tracked in real time cross country on theranch. For example, assuming that each of square-shaped master coverageareas 194 of FIG. 7 are four miles across in dimension (10,240 acres),an aggregate coverage area 702 of 20 miles across (256,000 acres) may beestablished for tracking freely roaming aRFID tags 180 therein. Otherexample applications include, but are not limited to, large areas ofrural and/or urban landscapes. In this regard, an aRFID communicationsystem 700 having an aggregate coverage area made up of multiple smallermaster coverage areas 194 may be used to monitor and track movement oftagged goods or vehicles across a national or state highways (e.g., suchas movement of trucked cargo, road maintenance vehicles, law enforcementvehicles, etc.), for example, using cell towers, utility poles or signsas platforms for aRFIDI systems 190 and UWB receiver antennas 160. Inanother example, tagged goods within a warehouse or multiple warehouseslocated in an urban landscape (e.g., section of a city) may be trackedin real time using a grid of master coverage areas 194 that are laid outon a city block or larger basis, e.g., using towers or pre-existinglocal building tops as mounting platforms for aRFIDI systems 190 and UWBreceiver antennas 160. In such an implementation, movement of goodswithin the aggregate coverage area 702 formed by the multiple mastercoverage areas 194 may be tracked in real time, e.g., movement of cargoinside one or more warehouse/s, movement of cargo into or out from awarehouse on trucks, etc. Such an implementation may be used toalternatively or additionally track any other types of objects, e.g.,police vehicles, delivery vans, school buses, etc.

Further information on possible tracking applications that may beimplemented using embodiments of the disclosed systems and methods maybe found, for example, in concurrently filed provisional U.S. patentapplication Ser. No. ______ entitled “RFID SYSTEMS AND METHODS” by KenA. Stroud, et. al., which is filed on the same date as the presentapplication and which is incorporated herein by reference in itsentirety.

FIG. 8 is a block diagram of one exemplary embodiment of a dataprocessing network system (e.g., UWB data processing network system 800in this embodiment) that may be employed to perform real time trackingof aRFID tags 180 that exist in an aggregate coverage area environmentthat includes multiple master coverage areas, for example, such asillustrated and described in relation to FIG. 7. As shown in FIG. 8,router circuitry 802 may be provided and coupled to receive digitalreceiver data signals 512 a to 512 n from each of corresponding UWBreceivers 502 a to 502 n that are in turn coupled to receive UWBresponse signal transmissions 510 a to 510 n via respective. UWBreceiver antennas 160 a to 160 n, in a manner similar to described inrelation to the single master coverage area embodiment of FIG. 6. UWBreceiver antennas 160 a to 160 n each may correspond to one of the 36UWB receiver antennas illustrated in FIG. 7 (i.e., n=36). Routercircuitry 802 is also shown coupled to data processing circuitrycomponents (e.g., UWB processing circuitries 504 a to 504 x in thisembodiment), which each may correspond to one of the 25 master coverageareas of FIG. 7 (i.e., x=25) and which may each perform similarprocessing tasks as UWB processing circuitry 504 of FIG. 6. Routercircuitry 802 in turn operates to route four selected digital receiverdata signals 512 (i.e., selected from digital receiver data signals 512a to 512 n) corresponding to one of the 25 master coverage areas 194 ofFIG. 7 to one of the UWB processing circuitry components 504 a to 504 x,e.g., based on source and/or destination information contained in thepacket headers of data signals 512. Thus, each one of UWB processingcircuitry components 504 a to 504 x is configured to correspond to oneof the 25 master coverage areas 194 of FIG. 7, and to performmultilateration or hyperbolic positioning calculations (and/or otherdata processing operations) for its corresponding master coverage area194.

Still referring to FIG. 8, each of UWB processing circuitry components504 a to 504 x provides respective digital processed tag information 514a to 514 x (e.g., tag location coordinates, collected and/or processedsensor information, etc.) to database engine circuitry 804 which may be,for example, a personal computer, server, etc. In this regard, each oneof signals 514 a to 514 x corresponds to processed tag information for agiven respective one of master coverage areas 194. Database enginecircuitry 804 may include one or more processors and other hardwareconfigured to provide display signals 812 to one or more displaydevice/s 808, e.g., to implement a graphical user interface (GUI) ondisplay device/s 808 that allows a user to interact with database engine804 for tasks such as historical and real-time tracking of locations ofindividual aRFID tags 180, viewing and manipulating collectedtag-related sensor data, etc.

As shown in FIG. 8, database engine circuitry 804 may also be coupled toone or more storage device/s 806 (e.g., magnetic or optical disk drives,solid state memory, etc.) for storing tag information 810, such as pasttag location coordinates and reported sensor data. An optional networkconnection 814 may be provided to allow access to database engine 804 tousers across a network 820, e.g., external public access network such asthe Internet, internal corporate or government network, etc. In oneexemplary embodiment, network access may be so provided so thatparticular users are given the ability to access particular types ofdata and/or data from particular aRFID tags 180 or master coverage areas194, without the ability to access other types of data and/or data fromother aRFID tags 180 or other master coverage areas 194. In this way,information from aRFID tags 180 that are associated with different typesof objects and/or located in different master coverage areas 194 may bemonitored in a common aggregate coverage area 702, but informationassociated therewith may be selectively monitored or retrieved bydifferent users, e.g., different customers of the operator of an aRFIDcommunication system 700 having an aggregate coverage area 702 such asillustrated and described in relation to FIG. 7. It is also possiblethat similar selective data access may be provided for individual usersof an aRFID communication system 100 having a single master cover area194 such as illustrated and described in relation to FIG. 1.

It will be understood that one or more of the tasks, functions, ormethodologies described herein may be implemented, for example, asfirmware or other computer program of instructions embodied in atangible computer readable medium that is executed by a CPU,microcontroller, or other suitable processing device.

While the invention may be adaptable to various modifications andalternative forms, specific embodiments have been shown by way ofexample and described herein. However, it should be understood that theinvention is not intended to be limited to the particular formsdisclosed. Rather, the invention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theinvention as defined by the appended claims. Moreover, the differentaspects of the disclosed systems and methods may be utilized in variouscombinations and/or independently. Thus the invention is not limited toonly those combinations shown herein, but rather may include othercombinations.

1. A method of operating a radio frequency identification (RFID) tagwithin a radio frequency identification (RFID) communicationenvironment, comprising: providing at least one RFID tag configured toreceive periodic first band RF signal interrogator polling signals andconfigured to transmit second band RF signal response signals inresponse thereto, the first band being a multiple channel-basedfrequency band and the second band being a non-channel based frequencyband; and repeatedly and alternately performing the following two steps:operating the RFID tag in a timed low power sleep mode for a predefinedsleep time during which the RFID tag does not listen for transmittedfirst band RF signal interrogator polling signals, and then waking theRFID tag to operate in a timed powered up listening mode for apredefined tag listening time during which the RFID tag actively listensfor transmitted first band RF signal interrogator polling signals; andwherein the method further comprises dynamically adjusting the length ofthe predefined sleep time before again waking the RFID tag to thelistening mode.
 2. The method of claim 1, further comprising dynamicallyadjusting the length of the predefined sleep time before again wakingthe RFID tag to listening mode based upon at least one of the time ofreceipt of a periodic interrogator polling signal during the listeningmode, the non-receipt of a periodic polling signal during the listeningmode, or a combination thereof.
 3. The method of claim 1, wherein themethod further comprises dynamically adjusting the length of thepredefined sleep time in at least one of the following manners:receiving a periodic interrogator polling signal at the RFID tag at agiven receipt time while the RFID tag is operating in the listening modeand increasing or decreasing the length of the predefined sleep timebased on the given receipt time of the interrogator polling signal asnecessary to maintain a predefined alignment time between the start timeof the listening mode and the given receipt time of the latest periodicinterrogator polling signal, not receiving an interrogator pollingsignal at the RFID tag while the RFID tag is operating in the listeningmode and decreasing the length of the predefined sleep time by anincremental amount of time before again operating the RFID tag inlistening mode, or a combination thereof.
 4. The method of claim 1,wherein the method further comprises dynamically adjusting the length ofthe predefined sleep time to maintain a predefined receive buffer time;wherein the predefined receive buffer time represents the latest timeelapsed between the time of waking the RFID tag to operate in a timedpowered up listening mode and the time of receipt of a firstinterrogator packet thereafter.
 5. The method of claim 1, furthercomprising operating the RFID tag in a synchronized state with periodicinterrogator signals by repeatedly and alternately performing thefollowing steps: operating the RFID tag in a timed synchronized lowpower sleep mode for a predefined synchronized sleep time during whichthe RFID tag does not listen for transmitted first band RF signalinterrogator polling signals; then waking the RFID tag to operate in atimed powered up synchronized listening mode for a predefinedsynchronized tag listening time during which the RFID tag activelylistens for transmitted first band RF signal interrogator pollingsignals; wherein the method further comprises performing the followingsteps if an interrogator polling signal is received during a givensynchronized listening mode: processing the latest received interrogatorpolling signal, performing one or more tag processing operations,increasing or decreasing the length of the predefined synchronized sleeptime based on the given receipt time of the interrogator polling signalas necessary to maintain a predefined alignment time between the starttime of the synchronized listening mode and the given receipt time ofthe periodic interrogator polling signal, and returning the RFID tag tothe timed synchronized low power sleep mode for the predefinedsynchronized sleep time; and wherein the method further comprisesperforming the following steps if an interrogator polling signal is notreceived during a given synchronized listening mode: decreasing thelength of the predefined synchronized sleep time by an incrementalamount of time, performing one or more tag processing operations, andreturning the RFID tag to the timed synchronized low power sleep modefor the predefined synchronized sleep time if the number of consecutivetimes that an interrogator polling signal has not been received is lessthan a predefined threshold, or operating the RFID tag in annon-synchronized state with any periodic interrogator polling signals ifthe number of consecutive times that an interrogator polling signal hasnot been received is greater than a predefined threshold.
 6. The methodof claim 5, wherein the duration of the predefined synchronized tagsleep time is less than a predefined value of the frequency of theinterrogator polling signals.
 7. The method of claim 6, wherein theduration of the predefined synchronized tag sleep time is substantiallyequal to a predefined value of the frequency of the interrogator pollingsignals less a predefined receive buffer value and less the time forsignal and tag processing operations.
 8. The method of claim 5, whereinoperating the RFID tag in an non-synchronized state with any periodicinterrogator polling signals comprises repeatedly and alternatelyperforming the following steps: operating the RFID tag in a timednon-synchronized low power sleep mode for a predefined non-synchronizedsleep time during which the RFID tag does not listen for transmittedfirst band RF signal interrogator polling signals; then waking up theRFID tag to perform one or more tag processing operations; thenreturning the RFID tag to the timed non-synchronized low power sleepmode for the predefined non-synchronized sleep time if the number ofimmediately previous consecutive sleep times is less than a predefinedthreshold, or operating the RFID tag in a timed powered upnon-synchronized listening mode for a predefined non-synchronized taglistening time during which the RFID tag actively listens fortransmitted first band RF signal interrogator polling signals if thenumber of immediately previous consecutive sleep times is greater thanor equal to a predefined threshold.
 9. The method of claim 8, whereinthe duration of the predefined non-synchronized tag listening time isgreater than or equal to a predefined value of the frequency of theinterrogator polling signals.
 10. The method of claim 8, furthercomprising then again operating the RFID tag in the synchronized stateupon receipt of a periodic interrogator polling signal during thenon-synchronized tag listening time of the non-synchronized listeningmode.
 11. The method of claim 1, wherein the first band is a narrow bandfrequency modulation (NBFM) frequency band; and wherein the second bandis an ultra-wideband (UWB) frequency band.
 12. A frequencyidentification (RFID) tag system, comprising: first band receiver ortransceiver circuitry configured to receive periodic first band RFsignal interrogator polling signals and second band transmittercircuitry configured to transmit second band RF signal response signalsin response thereto, the first band being a multiple channel-basedfrequency band and the second band being a non-channel based frequencyband; and at least one processing device to repeatedly and alternatelyperform the following two steps: operate the circuitry of the RFID tagin a timed low power sleep mode for a predefined sleep time during whichthe first band receiver or transceiver circuitry does not listen fortransmitted first band RF signal interrogator polling signals, then wakeup circuitry of the RFID tag to operate in a timed powered up listeningmode for a predefined tag listening time during which the first bandreceiver or transceiver circuitry actively listens for transmitted firstband RF signal interrogator polling signals, and dynamically adjust thelength of the predefined sleep time before again waking circuitry of theRFID tag to the listening mode.
 13. The system of claim 12, wherein theat least one processing device is further configured to dynamicallyadjust the length of the predefined sleep time before again waking thefirst band receiver or transceiver circuitry to listening mode basedupon at least one of the time of receipt of a periodic interrogatorpolling signal during the listening mode, the non-receipt of a periodicpolling signal during the listening mode, or a combination thereof. 14.The system of claim 12, wherein the at least one processing device isfurther configured to dynamically adjust the length of the predefinedsleep time in at least one of the following manners: increasing ordecreasing the length of the predefined sleep time based on the givenreceipt time of the interrogator polling signal while the RFID tag isoperating in the listening mode as necessary to maintain a predefinedalignment time between the start time of the listening mode and thegiven receipt time of the latest periodic interrogator polling signal,decreasing the length of the predefined sleep time by an incrementalamount of time before again operating the RFID tag in listening modeupon not receiving an interrogator polling signal at the RFID tag whilethe RFID tag is operating in the listening mode, or a combinationthereof.
 15. The system of claim 12, wherein the at least one processingdevice is further configured to dynamically adjust the length of thepredefined sleep time to maintain a predefined receive buffer time;wherein the predefined receive buffer time represents the latest timeelapsed between the time of waking the first band receiver ortransceiver circuitry of the RFID tag to operate in a timed powered uplistening mode and the time of receipt of a first interrogator packetthereafter.
 16. The system of claim 12, wherein the at least oneprocessing device is further configured to operate the RFID tag in asynchronized state with periodic interrogator signals by repeatedly andalternately performing the following steps: operating circuitry of theRFID tag in a timed synchronized low power sleep mode for a predefinedsynchronized sleep time during which the first band receiver ortransceiver circuitry does not listen for transmitted first band RFsignal interrogator polling signals; then waking the circuitry of theRFID tag to operate in a timed powered up synchronized listening modefor a predefined synchronized tag listening time during which the firstband receiver or transceiver circuitry actively listens for transmittedfirst band RF signal interrogator polling signals; performing thefollowing steps if an interrogator polling signal is received during agiven synchronized listening mode: processing the latest receivedinterrogator polling signal, performing one or more tag processingoperations, increasing or decreasing the length of the predefinedsynchronized sleep time based on the given receipt time of theinterrogator polling signal as necessary to maintain a predefinedalignment time between the start time of the synchronized listening modeand the given receipt time of the periodic interrogator polling signal,and returning the RFID tag to the timed synchronized low power sleepmode for the predefined synchronized sleep time; and performing thefollowing steps if an interrogator polling signal is not received duringa given synchronized listening mode: decreasing the length of thepredefined synchronized sleep time by an incremental amount of time,performing one or more tag processing operations, and returningcircuitry of the RFID tag to the timed synchronized low power sleep modefor the predefined synchronized sleep time if the number of consecutivetimes that an interrogator polling signal has not been received is lessthan a predefined threshold, or operating the RFID tag in anon-synchronized state with any periodic interrogator polling signals ifthe number of consecutive times that an interrogator polling signal hasnot been received is greater than a predefined threshold.
 17. The systemof claim 16, wherein the duration of the predefined synchronized tagsleep time is less than a predefined value of the frequency of theinterrogator polling signals.
 18. The system of claim 17, wherein theduration of the predefined synchronized tag sleep time is substantiallyequal to a predefined value of the frequency of the interrogator pollingsignals less a predefined receive buffer value and less the time forsignal and tag processing operations.
 19. The system of claim 16,wherein the at least one processing device is further configured tooperate the RFID tag in a non-synchronized state with any periodicinterrogator polling signals comprises repeatedly and alternatelyperforming the following steps: operating circuitry of the RFID tag in atimed non-synchronized low power sleep mode for a predefinednon-synchronized sleep time during which the first band receiver ortransceiver circuitry does not listen for transmitted first band RFsignal interrogator polling signals; then waking circuitry of the RFIDtag to perform one or more tag processing operations; then returningcircuitry of the RFID tag to the timed non-synchronized low power sleepmode for the predefined non-synchronized sleep time if the number ofimmediately previous consecutive sleep times is less than a predefinedthreshold, or operating the RFID tag in a timed powered upnon-synchronized listening mode for a predefined non-synchronized taglistening time during which the first band receiver or transceivercircuitry actively listens for transmitted first band RF signalinterrogator polling signals if the number of immediately previousconsecutive sleep times is greater than or equal to a predefinedthreshold.
 20. The system of claim 19, wherein the duration of thepredefined non-synchronized tag listening time is greater than or equalto a predefined value of the frequency of the interrogator pollingsignals.
 21. The system of claim 19, wherein the at least one processingdevice is further configured to again operate the RFID tag in thesynchronized state upon receipt of a periodic interrogator pollingsignal during the non-synchronized tag listening time of thenon-synchronized listening mode.
 22. The system of claim 12, wherein thefirst band is a narrow band frequency modulation (NBFM) frequency band;and wherein the second band is an ultra-wideband (UWB) frequency band.23. A method of operating a radio frequency identification (RFID) tagwithin a radio frequency identification (RFID) communicationenvironment, comprising: alternately operating at least one RFID tagbetween a non-synchronized state with a periodic interrogator pollingsignal and a synchronized state with a periodic interrogator pollingsignal, the RFID tag being configured to receive periodic first band RFsignal interrogator polling signals and to transmit second band RFsignal response signals in response thereto, the first band being amultiple channel-based frequency band and the second band being anon-channel based frequency band; wherein in the non-synchronized stateof the method comprises: operating the RFID tag in a timednon-synchronized low power sleep mode for a predefined non-synchronizedsleep time during which the RFID tag does not listen for transmittedfirst band RF signal interrogator polling signals, then waking up theRFID tag to perform one or more tag processing operations, thenreturning the RFID tag to the timed non-synchronized low power sleepmode for the predefined non-synchronized sleep time if the number ofimmediately previous consecutive sleep times is less than a predefinedthreshold, or operating the RFID tag in a timed powered upnon-synchronized listening mode for a predefined non-synchronized taglistening time during which the RFID tag actively listens fortransmitted first band RF signal interrogator polling signals if thenumber of immediately previous consecutive sleep times is greater thanor equal to a predefined threshold; and wherein in the synchronizedstate of the method comprises: operating the RFID tag in a timedsynchronized low power sleep mode for a predefined synchronized sleeptime during which the RFID tag does not listen for transmitted firstband RF signal interrogator polling signals, then waking up the RFID tagto operate in a timed powered up synchronized listening mode for apredefined synchronized tag listening time during which the RFID tagactively listens for transmitted first band RF signal interrogatorpolling signals, performing the following steps if an interrogatorpolling signal is received during a given synchronized listening mode:processing the latest received interrogator polling signal, performingone or more tag processing operations, increasing or decreasing thelength of the predefined synchronized sleep time based on the givenreceipt time of the interrogator polling signal as necessary to maintaina predefined alignment time between the start time of the synchronizedlistening mode and the given receipt time of the periodic interrogatorpolling signal, and then returning the RFID tag to the timedsynchronized low power sleep mode for the predefined synchronized sleeptime, and performing the following steps if an interrogator pollingsignal is not received during a given synchronized listening mode:decreasing the length of the predefined synchronized sleep time by anincremental amount of time, performing one or more tag processingoperations, and then returning the RFID tag to the timed synchronizedlow power sleep mode for the predefined synchronized sleep time if thenumber of consecutive times that an interrogator polling signal has notbeen received is less than a predefined threshold, or then operating theRFID tag in the non-synchronized state if the number of consecutivetimes that an interrogator polling signal has not been received isgreater than a predefined threshold.
 24. The method of claim 23, whereinthe first band is a narrow band frequency modulation (NBFM) frequencyband; and wherein the second band is an ultra-wideband (UWB) frequencyband.
 25. A frequency identification (RFID) tag system, comprising:first band receiver or transceiver circuitry configured to receiveperiodic first band RF signal interrogator polling signals and secondband transmitter circuitry configured to transmit second band RF signalresponse signals in response thereto, the first band being a multiplechannel-based frequency band and the second band being a non-channelbased frequency band; and at least one processing device to repeatedlyand alternately operate the RFID tag between a non-synchronized statewith a periodic interrogator polling signal and a synchronized statewith a periodic interrogator polling signal; wherein in thenon-synchronized state the at least one processing device is configuredto: operate the first band receiver or transceiver circuitry of the RFIDtag in a timed non-synchronized low power sleep mode for a predefinednon-synchronized sleep time during which the first band receiver ortransceiver circuitry does not listen for transmitted first band RFsignal interrogator polling signals, then wake up the first bandreceiver or transceiver circuitry to perform one or more tag processingoperations, then return the first band receiver or transceiver circuitryto the timed non-synchronized low power sleep mode for the predefinednon-synchronized sleep time if the number of immediately previousconsecutive sleep times is less than a predefined threshold, or operatethe first band receiver or transceiver circuitry in a timed powered upnon-synchronized listening mode for a predefined non-synchronized taglistening time during which the first band receiver or transceivercircuitry actively listens for transmitted first band RF signalinterrogator polling signals if the number of immediately previousconsecutive sleep times is greater than or equal to a predefinedthreshold; and wherein in the synchronized state the at least oneprocessing device is configured to: operate the first band receiver ortransceiver circuitry in a timed synchronized low power sleep mode for apredefined synchronized sleep time during which the first band receiveror transceiver circuitry does not listen for transmitted first band RFsignal interrogator polling signals, then wake the first band receiveror transceiver circuitry to operate in a timed powered up synchronizedlistening mode for a predefined synchronized tag listening time duringwhich the first band receiver or transceiver circuitry actively listensfor transmitted first band RF signal interrogator polling signals,perform the following steps if an interrogator polling signal isreceived during a given synchronized listening mode: process the latestreceived interrogator polling signal, perform one or more tag processingoperations and increase or decrease the length of the predefinedsynchronized sleep time based on the given receipt time of theinterrogator polling signal as necessary to maintain a predefinedalignment time between the start time of the synchronized listening modeand the given receipt time of the periodic interrogator polling signal,and then return the RFID tag to the timed synchronized low power sleepmode for the predefined synchronized sleep time, and perform thefollowing steps if an interrogator polling signal is not received duringa given synchronized listening mode: decrease the length of thepredefined synchronized sleep time by an incremental amount of time andperform one or more tag processing operations, and then return circuitryof the RFID tag to the timed synchronized low power sleep mode for thepredefined synchronized sleep time if the number of consecutive timesthat an interrogator polling signal has not been received is less than apredefined threshold, or then operate the RFID tag in thenon-synchronized state if the number of consecutive times that aninterrogator polling signal has not been received is greater than apredefined threshold.
 26. The system of claim 25, wherein the first bandis a narrow band frequency modulation (NBFM) frequency band; and whereinthe second band is an ultra-wideband (UWB) frequency band.